The present invention relates to a glazing comprising:                a substrate made of coloured soda-lime glass composed of main glass-forming constituents and of colouring agents,        a coating deposited on the coloured glass substrate.        
The expression “soda-lime glass” is used here in the broad sense and relates to any glass which comprises the following constituents (percentages by weight):
SiO260 to 75%Na2O10 to 20%CaO 0 to 16%K2O 0 to 10%MgO 0 to 10%Al2O30 to 5%BaO0 to 2%BaO + CaO + MgO10 to 20%K2O + Na2O 10 to 20%.
This type of glass finds very wide use in the field of glazings for motor vehicles or buildings, for example. It is commonly manufactured in the form of a ribbon by the float-glass process. Such a ribbon can be cut in the form of sheets, which can subsequently be bent or subjected to a treatment for enhancing the mechanical properties, for example a thermal tempering treatment.
When referring to the optical properties of a glass sheet, it is generally necessary to relate these properties to a standard illuminant. In the present description, two standard illuminants are used: Illuminant C and Illuminant A defined by the Commission Internationale de l'Eclairage (C.I.E.) [International Commission on Illumination]. Illuminant C represents average daylight having a colour temperature of 6700 K. This illuminant is especially of use in evaluating the optical properties of glazings intended for buildings. Illuminant A represents the radiation from a Planck radiator at a temperature of approximately 2856 K. This illuminant represents the light emitted by car headlamps and is especially intended to evaluate the optical properties of glazings intended for motor vehicles.
The “light transmission factor” (LT) is the percentage of incident luminous flux transmitted in the visible region, between 380 and 780 nm, through a substrate.
The “light reflection factor” (LR) is the percentage of incident luminous flux reflected by a substrate.
The “ultraviolet transmission factor” (UVT4) is the total percentage of transmission in the ultraviolet, between 290 nm and 380 nm, for a glass with a thickness of 4 mm.
The “energy transmission factor” (ET) is the total percentage of incident energy radiation directly transmitted through a substrate between the wavelengths 300 and 2500 nm.
The “solar factor” (SF) is the sum of the total energy directly transmitted through a substrate (ET) and of the energy which is absorbed (AE) and reradiated at the face opposite the energy source, with respect to the total energy radiation reaching the substrate.
The “selectivity” of a coated substrate represents the ratio between the light transmission factor and the energy transmission factor. It can be defined as being the ratio of the light transmission factor to the solar factor (LT/SF), which is used in particular in the case of a building glazing. It can also be defined as being the ratio of the light transmission factor to the energy transmission factor (LT/ET), in particular in the case of glazings for vehicles, for which the energy which is absorbed and reradiated is regarded as negligible when the vehicle is in motion.
The “dominant wavelength” (λD) is the peak wavelength in the range transmitted or reflected by the coated substrate.
The “purity” (P) of the colour of the substrate refers to the excitation purity measured using Illuminant C. It is defined according to a linear scale in which a defined source of white light has a purity of 0 and the pure colour has a purity of 100%. The purity of a coated substrate is measured on the side opposite the coated face.
The “emissivity” (ε) is the ratio of the energy emitted by a given surface at a given temperature to that of a perfect radiator (black body having an emissivity of 1.0) at the same temperature.